Response Of Composite Sandwich Panels Research Articles

In-plane compressive response of composite sandwich panels with local-tight honeycomb cores

In the present study, honeycomb cores with periodic tight zones were proposed for carbon-fiber and aluminum-honeycomb sandwich panels by flattening hexagon-shaped cells of honeycomb walls. In-plane compression tests were performed for sandwich panels with three types of local-tight honeycomb cores to evaluate the effects of the local-tight configurations on mechanical properties and failure modes. Experimental results indicated that the mechanical properties of sandwich specimens were effectively increased by using the proposed local-tight honeycomb cores. In particular, the specific energy absorption of sandwich specimens with a local-orthogonal-tight core was increased by 400.46%. In addition, Digital Image Correlation (DIC) technique was employed to further investigate the compressive behaviors of the sandwich specimens with and without local-orthogonal-tight honeycomb cores. The experimental measurements and detailed DIC observations indicated that the local-orthogonal-tight honeycomb core sandwich structures, which provided improved load transferring paths and reduced mismatch between the high-stiffness face sheets and low-stiffness core, exhibited progressive crushing failure modes.

Vibro-Acoustic Behavior of Rubber Filled Composite Sandwich Panel

This paper investigates the vibro-acoustic behavior of composite sandwich panels with different cellular sandwich cores. In these designs, two face sheets are made of carbon/ glass hybrid fiber bonded to the hexagonal honeycombs or chiral structure, and the filler is thermoplastic vulcanized rubber. Numerical simulation and model experiments are performed to obtain the vibration and sound radiation of composite sandwich panels with and without rubber. It is found that numerical results including vibration acceleration and sound pressure agree well with the corresponding experimental results. The analysis shows that the rubber filler is able to effectively reduce the vibro-acoustic response of composite sandwich panels. The effect of cellular sandwich core parameters on the vibration and sound radiation of composite sandwich panels is also discussed, which proves that the chiral structure can present superior dynamic properties.

Bending response of sandwich panels with steel skins and aluminium foam core

AbstractNominated for Eurosteel 2021 Best Paper AwardThe introduction to the market of metal foams represents a significant opportunity to increase the use of metal in the construction market. In fact, the development of new products made of metal foams and steel could improve the performance of conventional buildings in terms of stiffness and resistance. The first structural applications of these materials have already shown the potential of composites made of foam and steel, and demonstrated the feasibility of producing mono‐dimensional and bi‐dimensional elements with a high resistance‐to‐weight ratio. Reducing the structural weight can be a significant advantage in many cases, such as infrastructures or buildings in seismic zones. Within this framework, the work presented in this paper aims to assess the response of composite sandwich panels made of steel and aluminium foam using a set of tests that will serve as the basis for developing a new system of dry‐assembled composite floors. The tests were carried out at the Strength laboratory (Structural Engineering Test Hall) at the University of Salerno, Italy and were designed to verify the mechanical properties of metal foam panels and double‐skin glued sandwich panels. The tests have shed light on the basic mechanical properties of both foams and sandwich panels.

A layer-wise formulation for transient response of composite sandwich panel in the exposure of thermal shock loading by considering novel linear and torsional elastic foundation

In order to present practical ways to decline the adverse effects of thermal shock loading from the perspective of improving structural design, authors of this study put their main focus on the analysis of transient coupled poro-thermo-elastic behavior of the sandwich cylindrical panel under multi-directional initially stresses with functionally graded carbon nanotube reinforced (FG-CNTRC) face-layers and polymeric core resting on novel elastic foundation. With the aid of compatibility conditions, the sandwich structure with three layers are modeled. To guarantee the accuracy of the calculations, authors define the governing equations of the system within the context of the exact three-dimensional form of elasticity theory. Additionally, the Navier approach is employed as the analytical solution to find the response of the simply-supported structure in the content of shear stresses and transverse deflection. Dubner and Abate method is utilized to inverse the Laplace transform in order to determine the time history of the system. Convergence of the stress and deflections of the system with respect to passing time is examined and verified. The parametric study reveals that utilizing each of the CNT scattering patterns through the radial direction of the face-layers is useful for protecting specific proportion of the thickness against the applied thermal shock. Moreover, by tracking the effect of increasing the damper coefficient of the surrounding foundation on the different components of the stress, it is revealed that increasing this factor leads to increase of the transverse shear stress and decrease of the normal shear stress.

Bending response of three‐layers sandwich panels with steel skins and aluminium foam core

AbstractThe introduction in the market of metal foams represents a significant opportunity to increase the use of metal in the construction market. In fact, the development of new products made of metal foams and steel could allow improving the performances of conventional buildings in terms of stiffness and resistance. The first structural applications of these materials have already shown the potentialities of composites made of foam and steel, verifying the possibility to realize mono‐dimensional and bi‐dimensional elements with high resistance‐weight ratio. The reduction of the structural weight can represent a significant advantage in many cases, such as for buildings in seismic zone or infrastructures. Within this framework, the objective of the preliminary work presented in this paper is to analyze the response of composite sandwich panels made of steel and aluminium foam with a set of tests which will serve as the basis of development for a new system of dry assembled composite floors. The tests have been carried out at the laboratory StrEngTH of the University of Salerno, verifying the mechanical properties of only‐foam panels and of double skin glued sandwich panels. The tests have allowed to obtain the basic mechanical properties of both foams and sandwich panels.

Low-energy impact response of composite sandwich panels with thermoplastic honeycomb and reentrant cores

In the present study, the low-energy impact response of woven carbon fibre reinforced plastic (CFRP) composite sandwich panels with thermoplastic honeycomb and reentrant cores was investigated experimentally and numerically under three different impact energies (20 J, 40 J and 70 J). The Acrylonitrile Butadiene Styrene (ABS) honeycomb and reentrant core structures were manufactured in-plane and out-of-plane oriented via 3D printer, and adhesively bonded with two CFRP face sheets. The results indicate that the in-plane reentrant core based composite sandwich panel exhibits better impact strength and energy dissipation behavior than the in-plane and out-of-plane honeycomb core based composite sandwich panels.

Internal-structure-model based simulation research of aramid honeycomb sandwich panel subjected to intense impulse loading

An experimental investigation on the dynamic response of composite sandwich panels, comprising two titanium alloy plates and an aramid honeycomb core, subjected to intense impulse loading was carried out with the electric gun method. And brief results were presented within this paper. Based on the experiments, simulations were conducted with SPH-based internal structure model using the AUTODYN software. Here, the elasto-plastic constitutive was adopted to describe the mechanical behaviour of the core and corresponding matrix constitutive parameters were obtained quantitatively. An optimal particle size was determined by comparing the effects of different particle sizes on computational efficiency and accuracy. Afterwards, the proposed SPH model was validated with the experiments, making it feasible for following studies. To study the weakening effect of the core, a stress decay coefficient was proposed, and the results proved that the aramid honeycomb core played an important role in weakening the reflected tensile wave. Finally, the impact resistance assessment, in which three different forms of panels were compared, indicated that the aramid honeycomb sandwich panel was superior to the other two.

Compression and shear response of carbon fiber composite sandwich panels with pyramidal truss cores after thermal exposure

ABSTRACTThe composite pyramidal truss core sandwich panels with reinforced joints are manufactured by the water jet cutting and interlocking assembly method. The effect of thermal exposure on the out-of-plane compression and shear performances of composite sandwich panels is investigated experimentally. In particular, the out-of-plane compression and shear moduli and strengths of the structures after thermal exposure are predicted theoretically. Experimental results show that the out-of-plane compression and shear performances of composite pyramidal truss core sandwich panels first increase and then decrease with thermal exposure temperature at the thermal exposure of 6 h. The failure modes depend on the particular temperature and time of the applied thermal exposure. As well, the compression and shear performances first increase and then decease with thermal exposure time at 150°C. However, their compression and shear performances have a decreasing tendency with time for a given 230°C exposure temperature. In addition, the destruction responses of composite sandwich panels are also investigated and their possible failure modes (including the crushing, delamination and local buckling of struts) are complemented with the analytic results.

Experiments and numerical simulations of low‐velocity impact of sandwich composite panels

This article investigates the response of composite sandwich panel with Nomex honeycomb core subjected to low‐velocity impact and compression after impact (CAI) by using the methods of experiments and numerical simulations. Low‐velocity impact of sandwich panels at five energy levels is carried out to research the damage resistance and tolerance. A failure model based on Hashin failure criterion is implemented to model the intralaminar damage behavior of laminated plies in the numerical simulation. The cohesive zone model is used to simulate the delamination damage between adjacent laminated plies. The honeycomb core behavior is defined as an elastic–plastic material. Good agreements, in terms of contact‐force histories, damage shapes, and indentation depths of the sandwich panels, are observed between the experimental and numerical results. During CAI analysis, the damaged panels present a phenomenon of quick crack propagation from impact indentation location to each unloaded side after the structural strength reached. It is found that the in‐plane compressive strength of damaged sandwich panels is almost 25–35% reduction than that of undamaged panels. POLYM. COMPOS., 38:646–656, 2017. © 2015 Society of Plastics Engineers

High temperature indentation behaviors of carbon fiber composite pyramidal truss structures

The composite sandwich panels with pyramidal truss cores were fabricated by the hot-press method. Subsequently, the experimental studies were performed to investigate the quasi-static indentation response of composite sandwich panel at high temperature. The quasi-static indentation tests of composite sandwich panels were conducted at temperatures ranging from 20°C to 200°C. The damage mechanism, load–displacement curves, indentation load and absorbed energies at high temperature were investigated and compared with that at room temperature. The results showed that high temperature induced a change in the failure mechanism and had the significant effect on the load–displacement curves, indentation load and energy absorption. The indentation load and absorbed energies decreased as temperature increased. Especially at 200°C, the reduction in indentation load and absorbed energies was more severe, which was are mainly due to the degradation of matrix properties and fiber–matrix interface properties at higher temperature.

Low-velocity impact response of composite sandwich panels

In the present work, a detailed and rigorous theoretical approach was developed to investigate the impact response of composite sandwich panel subjected to low-velocity impact. The effect of the size of the impactor is included in the mathematical model. The theoretical approach uses the principle of minimum total potential energy to relate the deflection to the impact load. The internal energy comprising contact, bending and membrane energy together with the potential energy of the external work done were accounted for in the derivation of the load–displacement relationship of impactor with the composite sandwich panel. No perforation was accounted for in the present approach. Extensive impact tests were conducted and presented in some details. The comparison of the current approach with the experimental results showed that the trends of the impact response were predicted with some degree of confidence.

Mechanical Response of Composite Sandwich Panels: Deformation and Energy Absorption

The collapse modes and energy absorption in three-point bending of composite sandwich beams were explored experimentally. Sandwich beams manufactured from woven carbon fibre face sheets encapsulating aluminium foam cores were investigated at 0.001 s-1 and 100 s-1 strain rates. Three modes of failure were observed during deformation: Modes H1, H2 and H3. The direction of core shear played an important role in the energy absorption of the structure. Mode H2 gave rise to the highest specific energy absorption of the composite sandwich beams studied.

Pressure pulse response of composite sandwich panels with plastic core damping

An analytical technique is presented for obtaining the large amplitude, damped response of a foam-core composite sandwich panel subjected to uniform pressure pulse loading. The predicted panel response was in agreement with finite element analysis, and it was used to examine the blast resistance of panels with various foam cores. Although blast resistance generally increased with the increasing core density, panels with the densest cores exhibited no energy absorption before panel failure. The panel with the PVC H200 foam also sustained higher failure pressure per unit areal weight density than the denser panels with Klegecell R300 and HCP100 foams.

Composite sandwich structures for crashworthiness applications

Fibre-reinforced polymer sandwiches are promising materials for reducing vehicle mass, thereby improving the fuel economics. Nonetheless, to fully explore these materials as the primary structures and energy absorbers in vehicles, it is important to understand the energy absorption capabilities of these materials. Hence, in the present work, comprehensive experimental investigation on the response of composite sandwich panels to quasi-static compression has been carried out. The crashworthiness parameters, namely the peak load, absorbed crash energy, specific absorbed energy, average crushing load, stroke efficiency, and crush force efficiency of various types of composite sandwich panels were investigated in a series of edgewise compression tests. The composite sandwich panels tested consists of several designs, such as C-shaped, wrapped, and with composite inserts in the core of the panel. The tested composite sandwich specimens were primarily fabricated from glass fibre. For some of the designs, Kevlar and carbon fibres were used. For the core material, two different types of polymeric foams, polystyrene and polyurethane, were used with densities close to 30 kg/m3. Several modes of failure were observed and recorded. The primary mode of failure observed was progressive crushing with capabilities of high energy absorption and high stroke efficiencies. Particular attention is paid on the analysis of the mechanism of progressive crushing of the sandwich panels and its relation to the energy absorption capabilities. This is a vital information for designing these materials as energy absorbers.

Analytical Prediction of Low-velocity Impact Response of Composite Sandwich Panels using New TDOF Spring–mass–damper Model

A new equivalent three-degree-of-freedom (TDOF) spring–mass– damper (SMD) model has proposed to predict the low-velocity impact response of composite sandwich panels with transversely flexible core. Impacts are assumed to occur normally over the top face-sheet with the arbitrary different impactor masses and initial velocities. The interaction between the impactor and the panel is modeled with the help of a new proposed system having TDOF consisting of springs, damper, and masses. An analytical procedure that includes the transverse flexibility and structural damping of the core has not yet been dealt with. In the present model, the effects of transverse flexibility of the core and structural damping of the panel are considered analytically. The analysis yields analytic functions describing the history of contact force, displacements of the impactor and the panel in the transverse direction etc. The effects of some physical and geometrical parameters such as initial potential energy of the impactor, the aspect ratio of the panel, location of the impacted point on the panel and the material density of the core on dynamic response of composite sandwich panels have been discussed.

Dynamic Response of In-plane Pre-stressed Sandwich Panels with a Viscoelastic Flexible Core and Different Boundary Conditions

A new mathematical method and double Fourier series set of functions is developed to find out the local and global transverse and in-plane mode shapes, damped natural frequencies and modal loss factors in composite sandwich panels with multilayered laminated face sheets, viscoelastic flexible core and arbitrary boundary conditions. An improved high order sandwich plate theory (IHSAPT) is applied to investigate the dynamic behavior of fiber reinforced plastic (FRP) sandwich thin and thick panels. The present analysis is very general and valid for any type of core, any type of boundary conditions as well as for the cases where the conditions at the upper face sheet are different from those at the lower one along the same edge. Interaction between static in-plane initial stress and dynamic response of a sandwich panel are studied in this article. For different boundary conditions, solutions are obtained using the simple proposed identical double Fourier series functions and Stokes’s transformation technique. The effect of some parameters such as panel aspect ratio, thickness of core-thickness of panel ratio, and initial in-plane stresses on dynamic response of composite sandwich panel are discussed and studied in detail.

Higher-order dynamic response of composite sandwich panels with flexible core under simultaneous low-velocity impacts of multiple small masses

Small mass impactors, such as runway debris and hailstones may result in a wave controlled local response, which is essentially independent of boundary conditions. The higher-order impact model of sandwich beams presented by Mijia and Pizhong [Mijia, Y., Pizhong, Q., 2005. Higher-order impact modeling of sandwich structures with flexible core. International Journal of Solids and Structures 42 (10), 5460–5490] is developed and enhanced to impact analysis of sandwich panels with transversely flexible cores. Therefore, an improved fully dynamic higher-order impact theory is developed to analyze the low-velocity impact dynamic of a system which consists of a composite sandwich panel with transversely flexible core and multiple small impactors with small masses. Impacts are assumed to occur normally and simultaneously over the top face-sheet with arbitrary different masses and initial velocities of impactors. The contact forces between the panel and the impactors are treated as the internal forces of the system. First shear deformation theory (FSDT) is used for the face-sheets while three-dimensional elasticity is used for the soft core. The fully dynamic effects of the core layer and the face-sheets are considered in this study. Contact area can be varied with contact duration. The results in multiple mass impacts over sandwich panels that are hitherto not reported in the literature are presented based on proposed improved higher-order sandwich plate theory (IHSAPT). Finally, for the case study of the single mass impact, the numerical results of the analysis have been compared either with the available experimental results or with some theoretical results. As no literature could be found on the impact of multiple impactors over sandwich panels, the present formulation is validated indirectly by comparing the response of two cases of double small masses and single small mass impacts. Also, in order to demonstrate the applicability of the validation, the analytical relation of minimum distance between two impactors is derived based on Olsson’s wave control principle in this paper.

Finite element modelling of the crushing response of composite sandwich panels with FRP tubular reinforcements

The crushing response and the crash energy absorption characteristics of composite sandwich panels with internal fibre reinforced plastic (FRP) tubular reinforcements were investigated in the numerical simulation works described here using the LS-DYNA3D finite element code. Several models were developed in order to simulate a series of compressive tests performed at the National Technical University of Athens using composite sandwich panels with glass FRP faceplates and syntactic foam core that were internally reinforced with FRP tubes, and, moreover, to examine how the construction parameters of the sandwich panels influence the main crushing characteristics, i.e. the crash energy absorption and the peak compressive load. The sandwich construction parameters whose influence was investigated were the properties of some of the constituent materials (more specifically the foam core and the reinforcing FRP tubes) and the geometric characteristics of the internal reinforcements such as the thickness of the FRP tubes. The agreement between the finite element calculations and the experimental results was excellent concerning the load—displacement curve and the main crushing characteristics of the tested hybrid composite materials, as well as the overall crushing response of the sandwich panels in compressive loading, as a result of several refinements that were applied to the finite element models.

Response of composite sandwich panels with transversely flexible core to low-velocity transverse impact: A new dynamic model

A new computational procedure based on improved higher order sandwich plate theory (IHSAPT) and two models representing contact behavior between the impactor and the panel are adopted to study the low velocity impact phenomenon of sandwich panels comprising of a transversely flexible core and laminated composite face-sheets. The interaction between the impactor and the panel is modeled with the help of a new system having three-degrees-of-freedom, consisting of spring–mass–damper–dashpot (SMDD) or spring–mass–damper (SMD). The effects of transverse flexibility of the core, and structural damping are considered. The present analysis yields analytic functions describing the history of contact force as well as the deflections of the impactor and the panel in the transverse direction. In order to determine all components of the displacements, stresses and strains in the face-sheets and the core, a numerical procedure based on improved higher order sandwich plate theory (IHSAPT) and Galerkin's method is employed for modeling the layered sandwich panel (without the impactor), while the analytic force function developed on the basis of SMDD or SMD model, can be used for the contact force between the impactor and the panel. The contact force is considered to be distributed uniformly over a contact patch whose size depends on the magnitude of the impact load as well as the elastic properties and geometry of the impactor. Various boundary conditions for the sandwich panel have also been considered. Finally, the numerical results of the analysis have been compared either with the available experimental results or with some theoretical results.

Effect of physical and geometrical parameters on transverse low-velocity impact response of sandwich panels with a transversely flexible core

The effects of important physical and geometrical parameters on transverse low-velocity impact response of composite sandwich panels have been studied in this paper. Impacts are assumed to occur normally over the top and/or the bottom face sheets, at arbitrary locations and with different impactor masses and initial velocities. For deriving closed-form solutions for the contact force, displacements of the impactor and the panel in the transverse direction, the sandwich panel has been modeled as a discrete three-degrees-of-freedom dynamic system with equivalent masses and springs (SM). The dynamic response of the panel is based on the improved higher-order sandwich plate theory (IHSAPT) and both thick and thin panels have been analyzed. The effects of transverse flexibility of the core, and boundary conditions are considered. Also, the area of the contact patch between the impactor and the panel can be varied as it changes with contact duration. The numerical results of the analysis have been compared either with the available experimental results or with some theoretical results. It is established that the dynamic behavior of the sandwich panel depends on various parameters, such as the aspect ratio and the length-to-thickness ratio of the panel, core thickness, boundary conditions of the panel and impactor parameters like its potential energy, velocity and the location of contact point, etc.